1. Field of the Invention
The invention relates to access of information stored on an information storage medium such as a DVD (Digital Versatile Disc) or the like, and more particularly to access of control information such as synchronous signals, address information or the like.
2. Description of Related Art
Among bulk information storage media typified by DVD, on a DVD-R (DVD-Recordable) into which information can be written or a DVD-RW (DVD-ReWritable) in which information is rewritable, information is stored using groove tracks as information storage tracks. The groove track is interposed between land tracks, which are guide tracks for guiding a light source such as a laser beam or the like. When viewed from the light source, the groove tracks and the land tracks form convex portions and concave portions respectively. That is, the convex-concave tracks are formed along the circumference of an optical disk.
Furthermore, information on the attribute of stored information and information for attaining synchronization of data frames as a unit of stored information are stored as control information. This information is arranged on the land tracks which are not designed to store information, and is referred to as Land Pre Pit (hereinafter described as LPP) information.
In information storage media such as DVD-R, DVD-RW or the like, an information group of two kilo-bytes is configured as one data sector, and LPP information has a bit configuration with 13 bits as a unit for each data sector. FIG. 15 shows a bit configuration per data sector of LPP information. This is a configuration where a synchronous mark LSY is stored as the first bit of LPP information, where address bits indicating addresses among data sectors (hereinafter referred to as relative addresses) (Relative Addresses 3 to 0) are stored as the second to fifth bits of LPP information, and where data bits (Data 7 to 0) are stored as the sixth to thirteenth bits of LPP information. A one-bit-width synchronous mark LSY arranged at the head of a sector differs depending on differences among later-described 26 data frames (see FIG. 17) into which one data sector is divided. To be more specific, the data frames are numbered from 0. The data frames of even numbers are classified into an Even region, whereas the data frames of odd numbers are classified into an Odd region. In this instance, a synchronous mark LSY of xe2x80x9c111xe2x80x9d channel bits is set in the case of arrangement in a frame in the Even region, and a synchronous mark LSY of xe2x80x9c110xe2x80x9d channel bits is set in the case of arrangement in a frame in the Odd region. The synchronous mark LSY attains synchronization among sectors and determines whether a certain one of the frames belongs to the Even region or to the Odd region. Data are stored in all of the following 12 bits as xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d. On the medium, while bits xe2x80x9c0xe2x80x9d are denoted by xe2x80x9c100xe2x80x9d channel bits, bits xe2x80x9c1xe2x80x9d are denoted by xe2x80x9c101xe2x80x9d channel bits. The relative addresses of four bits, i.e. the second to fifth bits in the former half define the sequence of the sectors. Namely, as shown in FIG. 16, one data block is configured by taking together first to sixteenth sectors that have been identified continuously according to an ascending sequence as the addresses xe2x80x9c0000xe2x80x9d to xe2x80x9c1111xe2x80x9d. Parity and block addresses for error correction codes (ECC) are allocated to the other eight data bits, i.e. the sixth to thirteenth bits. One data block is divided into some sectors, and errors are detected and corrected as to data bit strings detected from a predetermined number of the sectors. As for bit strings of LPP information detected on the basis of a synchronous mark LSY, if consecutiveness of the relative addresses of four bits among the data sectors is confirmed and if it can be confirmed that the data bit strings are read out correctly owing to detection and correction of errors of the data bit strings in the predetermined number of sectors, it is concluded that access to LPP information has been made accurately. Thus, the readout state is locked.
FIG. 17 shows a track format of one data sector. As described above, one sector is divided into 26 data frames, which are numbered from 0. The frames of even numbers are classified into the Even region, whereas the frames of odd numbers are classified into the Odd region. Basically, LPP information is arranged bit by bit in the frames in the Even region. That is to say, a synchronous mark LSY is arranged in the zeroth frame, address bits are arranged in the second, fourth, sixth and eighth frames, and data bits are arranged in the tenth, twelfth, fourteenth, sixteenth, eighteenth, twentieth, twenty-second and twenty-fourth frames. On the other hand, the Odd region is secured as a spare data frame region. That is to say, the first frame is secured as a spare region for the synchronous mark LSY in the zeroth frame, the third, fifth, seventh and ninth frames are secured as spare regions for the address bits in the second, fourth, sixth and eighth frames respectively, and the eleventh, thirteenth, fifteenth, seventeenth, nineteenth, twenty-first, twenty-third and twenty-fifth frames are secured as spare regions for the data bits in the tenth, twelfth, fourteenth, sixteenth, eighteenth, twentieth, twenty-second and twenty-fourth frames respectively.
FIG. 18 shows a case where LPP information of the above track format is arranged on an information storage medium such as an optical disk or the like. LPP information is arranged on land tracks coincident with frame head positions of groove tracks on which information is stored. By irradiating the groove tracks formed along the circumference of the medium with light such as laser beams emitted from a light source, the information stored on the groove tracks is read out. At this moment, the spot radius of the light source is set greater than the width of the groove tracks so that some of the land tracks are also irradiated. Due to this configuration, the LPP information arranged on the land tracks is read out. LPP information is basically attached to each one of the data frames in the Even region and thus is arranged repeatedly at a pitch corresponding to two of the data frames on the disk. This arrangement is continuously repeated toward the center of the disk. Therefore, there is a fear that pieces of LPP information on two of the adjacent land tracks between which a corresponding one of the groove tracks is interposed may adjoin each other while overlapping with each other in a scanning direction of the light source. This hampers accurate read-out of LPP information. Thus, in general, in the case where pieces of LPP information overlap with each other, one of them is transferred to the Odd region, i.e. to an adjacent data frame. In this case, if the number of the data frame in the Odd region to which that piece of LPP information has been transferred is set as a number which is greater by one than the number of the data frame in the Even region to which that piece of information belongs intrinsically so that the Odd region is configured as a spare region for the Even region, those pieces of information can be prevented from overlapping with each other on the disk.
FIG. 19 shows an LPP access portion 1000 of the related art. Three-channel-bit LPP information read out by a light source is inputted to a three-channel-bit shift register 101. An LPP pattern comparing portion 102 subjects the LPP information inputted from the shift register 101 to comparison and finds out whether the LPP information coincides with xe2x80x9c111xe2x80x9d channel bits as a synchronous mark in the Even region, xe2x80x9c110xe2x80x9d channel bits as a synchronous mark in the Odd region, xe2x80x9c100xe2x80x9d channel bits indicating a data bit xe2x80x9c0xe2x80x9d, or xe2x80x9c101xe2x80x9d channel bits indicating xe2x80x9c1xe2x80x9d. If the LPP information coincides with a synchronous mark LSY, the LPP pattern comparing portion 102 outputs the synchronous mark LSY to a synchronous mark detecting portion 103. If the LPP information coincides with data bits, the LPP pattern comparing portion 102 outputs a data bit signal La/Ld indicating an address or data to a data detecting portion 105.
If a synchronous mark LSY is inputted to the synchronous mark detecting portion 103 from the LPP pattern comparing portion 102, the synchronous mark detecting portion 103 determines whether the inputted synchronous mark LSY is a synchronous mark xe2x80x9c111xe2x80x9d in a data frame in the Even region or a synchronous mark xe2x80x9c110xe2x80x9d in a data frame in the Odd region, and outputs a detection pulse SY. At the same time, the synchronous mark detecting portion 103 sets an initial counter value for a frame counter 106, which will be described later. That is, the counter initial value is set as 0 if the synchronous mark xe2x80x9c111xe2x80x9d corresponding to the Even region is detected, whereas the counter initial value is set as 1 if the synchronous mark xe2x80x9c110xe2x80x9d corresponding to the Odd region is detected.
Further, a least significant bit of the frame counter 106 is inputted to the synchronous mark detecting portion 103 as an Even/Odd identification signal F0. In one of data sector cycles following a cycle subsequent to detection of a synchronous mark, the synchronous mark detecting portion 103 detects the Even/Odd identification signal F0 and the synchronous mark LSY detected by the LPP pattern comparing portion 102. This is because of the necessity to adjust a count value of a later-described frame length counter 107 by a signal (not shown), change a count-up timing for the frame counter 106 and adjust a timing for detection in a subsequent data sector cycle for the purpose of fine adjustment of errors or the like in rotation control of an information storage medium such as a DVD-R or the like during access thereof.
The data detecting portion 105 demodulates the inputted three-channel-bit data bit signal La/Ld and outputs demodulated data Add/Data of xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d. The demodulated data Add/Data thus outputted are inputted to an address/data storage register 109.
The frame counter 106 counts data frame numbers 0 to 25 by enable signals transmitted to an enable terminal E. In the track format in one data sector shown in FIG. 17, the data frame number 0 indicates data frames in the Even region which are among the synchronous mark data frames and in which the synchronous mark xe2x80x9c111xe2x80x9d is stored. The data frame number 1 indicates data frames in the Odd region which are among the synchronous mark data frames and in which the synchronous mark xe2x80x9c110xe2x80x9d is stored. These data frame numbers 0 and 1 are outputted to the synchronous mark detecting portion 103 as an Even/Odd identification signal F0. Further, the data frame numbers 2 to 9 indicate data frames for four-bit relative addresses. These data frames are numbered with two data frames in the Even/Odd regions constituting one-bit storage region for each bit. Furthermore, the data frame numbers 10 to 25 indicate data frames for eight-bit data. These data frames are numbered with two data frames in the Even/Odd regions constituting one-bit storage region for each bit. Then the data frame numbers 2 and 25 are outputted to the data detecting portion 105 as address/data position signals FA/D.
The frame length counter 107 counts the number of clocks constituting frames by an enable signal transmitted to the enable terminal E and determines a count-up timing for the frame counter 106 by a count-up signal C.
The enable signal transmitted to the enable terminals E of the frame counter 106 and the frame length counter 107 is an output signal Q from a set-reset flip-flop (SRFF) 108. A detection signal SY from the synchronous mark detecting portion 103 is inputted to a set input S of the SRFF 108, whereas a reset signal RST is inputted to a reset input R of the SRFF 108.
Further, if a synchronous mark xe2x80x9c111xe2x80x9d is detected, it is determined that the synchronous mark xe2x80x9c111xe2x80x9d has been detected in a data frame in the Even region, and the initial count value of the frame counter 106 must be set as 0 (F1=0). If a synchronous mark xe2x80x9c110xe2x80x9d is detected, it is determined that the synchronous mark xe2x80x9c110xe2x80x9d has been detected in a data frame in the Odd region, and the initial count value of the frame counter 106 must be set as 1 (F0=1). This initial count value is set by a signal (not shown) from the synchronous mark detecting portion 103. Namely, if a synchronous mark LSY from the LPP pattern comparing portion 102 is detected, the initial value of the frame counter 106 is set as 0 (F0=0) in the case of detection of xe2x80x9c111xe2x80x9d and is set as 1 (F0=1) in the case of detection of xe2x80x9c110xe2x80x9d. In this manner, the data frames in which inputted LPP information is stored are made to conform to the frame counter values.
Further, in the case of a DVD-R, one data frame is configured of eight cycles of wobbling signals each of which consists of 186 bits. Thus, the frame length counter 107 is configured with its basic count value being 186xc3x978=1488. In fact, the above basic count value may cause deviation due to errors or the like in rotation control of an information storage medium such as a DVD-R or the like during access thereof. For this reason, a detection result of comparison between an Even/Odd identification signal F0 and a synchronous mark LSY detected in one of the data sector cycles following a cycle subsequent to detection of a synchronous mark from the synchronous mark detecting portion 103 is inputted as a signal (not shown) for fine adjustment of errors or the like. Thus, the count value is finely adjusted and a timing for detection in the subsequent data sector cycle is adjusted.
An operation of access LPP information will now be described with reference to FIG. 19. First of all, an initialized state in which a reset signal RST and the like have been inputted is realized. The SRFF 108 is in a reset state. A disable signal is inputted to the enable terminals E of the frame counter 106 and the frame length counter 107, and the counters 106, 107 have been reset and are out of operation. In this state, the LPP access portion 1000 is in a state of free-run. The Even/Odd identification signal F0 from the frame counter 106 has been initialized (F0=0), and the synchronous mark detecting portion 103 has been waiting to detect a synchronous mark xe2x80x9c111xe2x80x9d or xe2x80x9c110xe2x80x9d.
If a synchronous mark is detected by the LPP pattern comparing portion 102 with the frame counter 106 initialized, the synchronous mark detecting portion 103 sets the Even/Odd identification signal F0 at its initialized state in accordance with a signal from the synchronous mark detecting portion 103. That is, if a synchronous mark xe2x80x9c111xe2x80x9d is detected by the synchronous mark detecting portion 103, it is identified as a synchronous mark LSY in a data frame in the Even region, whereas if a synchronous mark xe2x80x9c110xe2x80x9d is detected by the synchronous mark detecting portion 103, it is identified as a synchronous mark LSY in a data frame in the Odd region. The count value of the frame counter 106 is initialized to 0 (F0=0) for a synchronous mark xe2x80x9c111xe2x80x9d in the Even region, and to 1 (F0=1) for a synchronous mark xe2x80x9c110xe2x80x9d in the Odd region.
Then a detection pulse SY is outputted, the SRFF 108 is set, and an output signal Q is outputted. The frame counter 106 and the frame length counter 107 are activated by the output signal Q. That is, if the frame length counter 107 reaches a count value corresponding to the length of one frame, i.e. if the timing for counting up has come, a count-up signal C is outputted to the frame counter 106 so that the count value of the frame counter 106 is incremented by one. The counting of 26 data frames constituting one data sector is carried out using count values of 0 to 25. The count value returns to 0 after having reached 25, and the same counting operation is repeated as to data frames in a subsequent data frame.
If operation of the frame counter 106 is finished, count values 2 to 25 as address/data position signals FA/D are outputted to a data detecting portion 105 and the address/data storage register 109. The data detecting portion 105 demodulates data in accordance with the address/data position signal FA/D, recognizes a data frame position to which the demodulated address belongs or the demodulated data belong, and also finds out whether the data frame is in the Even region or in the Odd region by referring to a data frame number. The demodulated address/data Add/Data is/are stored in the address/data storage register 109. It is then concluded through detection and correction of errors of the data and consecutiveness of the address that access to LPP information has been made. Thus, the following processes of access data are performed while securing a lock state.
Although LPP information is basically arranged in the frames in the Even region, it is preliminarily arranged in the frames in the Odd region only in the aforementioned case. Thus, in order to accurately reproduce 13-bit LPP information stored in one sector, it is important to carry out frame management based on correct detection of a synchronous mark LSY arranged in the first frame, including a clear distinction about whether the synchronous mark LSY is arranged in a frame in the Even region or in a frame in the Odd region. According to the related art, access to LPP information is made based on confirmation of consecutiveness of relative addresses and detection and correction of errors of data bits.
However, while LPP information is basically stored in the frames in the Even region which are arranged alternately with the frames in the Odd region, there may be some cases where LPP information is also stored preliminarily in some of the frames in the Odd region. Thus, if the type of a frame to which a synchronous mark LSY belongs is erroneously detected as the opposite type, an operation of access by the LPP access portion 1000 is performed normally with frames to be detected being deviant. This causes a fear that the existence of a lock state may be recognized. To be more specific, a synchronous mark xe2x80x9c111xe2x80x9d in the Even region may erroneously be detected as xe2x80x9c110xe2x80x9d, or a synchronous mark xe2x80x9c110xe2x80x9d in the Odd region may erroneously be detected as xe2x80x9c111xe2x80x9d. In both cases, the Even/Odd regions on the medium are reversely recognized by the LPP access portion 1000 as the Odd/Even regions. Also in this case, if xe2x80x9c111xe2x80x9d is erroneously detected as xe2x80x9c110xe2x80x9d for instance, LPP information in the Even region is detected as information in the Odd region. This causes a fear that apparent correctness in access of LPP information may be concluded as long as the LPP information is arranged in the Even region of the medium. The problem is that this deviation remains undetected until the LPP information on the medium is arranged in the Odd region.
Further, if LPP information is arranged in the Odd region on the medium, lack of LPP information in a specific one of the frames, dual access of LPP information in both the Even/Odd regions, or the like occurs. However, if access to LPP information cannot be made correctly because of the characteristics of the circuit configuration or the like of the LPP access portion 1000, a specific data value may be set as a default value. If this default value assumes a certain value, it is possible that the conditions for consecutiveness of relative addresses and detection and correction of errors of data bits may be satisfied, and that the data bits may be modified through the function of error correction. Therefore it is conceivable that detection of a deviation in access will take unnecessarily long. This causes a problem of the incapability to ensure good response and reliability in access LPP information.
Erroneous detection of the synchronous mark LSY mentioned above will be described in detail with reference to a concrete example shown in FIG. 20. FIG. 20 shows a case where a synchronous mark LSY of xe2x80x9c111xe2x80x9d channel bits in a frame in the Even region is detected as xe2x80x9c110xe2x80x9d channel bits. If a synchronous mark xe2x80x9c111xe2x80x9d is erroneously detected as xe2x80x9c110xe2x80x9d in a frame 0 in the Even region on the medium, it is erroneously recognized that the synchronous mark LSY has been confirmed in a frame in the Odd region. The count value of the frame counter 106 is preset as 1 and then incremented stepwise. Namely, the frame number managed by the frame counter 106 is greater by one than the number of a corresponding one of actual frames on the medium. This means an inverted relation between the Even and Odd regions.
An operation of detecting data is performed in accordance with the frame counter 106. Therefore, when a relative address 3 in the Even region is searched for with a count value 2 that has been incremented by one, the frame 1 in the Odd region on the medium is actually searched for. Because data and the like are basically arranged in the Even region, neither xe2x80x9c100xe2x80x9d indicating a bit xe2x80x9c0xe2x80x9d nor xe2x80x9c101xe2x80x9d indicating a bit xe2x80x9c1xe2x80x9d can be found. Thus, the count value of the frame counter 106 is again incremented by one and set as 3 so as to make a search in the Odd region. In this manner, the frame 2 in the Even region on the medium is actually detected. Because the relative address 3 is arranged in this region, the corresponding address bit is detected. The same operation is repeated thereafter.
Information that is intrinsically to be detected as LPP information in a frame in the Even region is erroneously found out in the Odd region. Also in this case, if original data are in the Even region, they can be detected as the same LPP information even with deviation of a detecting position to the Odd region. As a result, relative addresses can maintain consecutiveness thereof, and data bits are detected as normal bits. Thus, access to LPP information is made apparently correctly.
On the other hand, if a specific piece of LPP information is arranged in the Odd region on the medium (in the case of a frame 15 in FIG. 20A), data which are to be detected as data in the Odd region do not exist due to an instruction from the frame counter 106 (in the case of the frame counter value of 15 in FIG. 20B), and one-bit LPP information that is to be retrieved with a combination of the Even and Odd regions drops out (in the case of the frame counter value of 14 or 15 in FIG. 20B). To the contrary, if the frame counter value then assumes 16 and 17, LPP information data in the Odd region on the medium (the frame 15 shown in FIG. 20A) and LPP information data in the next frame in the Even region (the frame 16 shown in FIG. 20A) are read out. That is, two-bit LPP information is dually retrieved in two frames in the Even/Odd regions from which one-bit LPP information is to be retrieved. In this case, although the LPP access portion 1000 cannot detect LPP information correctly, there may be a case where access to LPP information is made apparently correctly if the aforementioned default value is set.
The invention has been made to solve the above problems of the related art. It is an object of the invention to provide an information access device, information access method and an information storage medium access system which can accurately reproduce a control information string by quickly and reliably detecting a deviation in frame management associated with erroneous detection of a synchronous mark and redetecting a synchronous mark when access control information on an information storage medium.
To achieve the above object, according to one aspect of the invention, there is provided an information access device that detects control information units at a synchronized timing based on detection of a specific control information unit included in a control information string when access the control information string that is added to an information unit composed of a predetermined number of data frame groups on an information storage medium and that has the control information units divided as basic units and stored in unit storage regions in which one of the data frames is a storage region and in which one or more of the other data frames are spare data frames for a spare region, wherein the control information unit includes a predetermined control information unit stored at a position of a predetermined one of the data frames in the data frame group, wherein the information access device comprises a setting portion for setting a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and a discordance detecting portion for detecting that the identifier in which the predetermined control information unit is detected does not correspond to the position of the predetermined one of the data frames, and wherein redetection of the specific control information unit is carried out based on an output from the discordance detecting portion.
Further, according to one aspect of the invention, there is provided an information access method in which control information units are detected at a synchronized timing based on detection of a specific control information unit included in a control information string when access the control information string that is added to an information unit composed of a predetermined number of data frame groups on an information storage medium and that has the control information units divided as basic units and stored in unit storage regions in which one of the data frames is a storage region and in which one or more of the other data frames are spare data frames for a spare region, wherein the control information unit includes a predetermined control information unit stored at a position of a predetermined one of the data frames in the data frame group, wherein the information access method comprises a setting step for setting a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and a discordance detecting step for detecting that the identifier in which the predetermined control information unit is detected does not correspond to the position of the predetermined one of the data frames, and wherein redetection of the specific control information unit is carried out based on an output from the discordance detecting step.
Further, according to one aspect of the invention, there is provided an information storage medium access system comprising a control information access portion that detects control information units at a synchronized timing based on detection of a specific control information unit included in a control information string when access the control information string that is added to an information unit composed of a predetermined number of data frame groups on an information storage medium and that has the control information units divided as basic units and stored in unit storage regions in which one of the data frames is a storage region and in which one or more of the other data frames are spare data frames for a spare region, wherein the control information unit includes a predetermined control information unit stored at a position of a predetermined one of the data frames in the data frame group, wherein the control information access portion comprises a setting portion for setting a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and a discordance detecting portion for detecting that the identifier in which the predetermined control information unit is detected does not correspond to the position of the predetermined one of the data frames, and wherein redetection of the specific control information unit is carried out based on an output from the discordance detecting portion.
In the information access device, the information access method and the information storage medium access system, the setting portion sets a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and the discordance detecting portion detects that the identifier in which the predetermined control information unit is detected does not correspond to the position of the predetermined one of the data frames. Redetection of the specific control information unit is carried out based on an output from the discordance detecting portion.
Thereby the corresponding identifier for each of the data frames is set on the basis of the data frame in which the specific control information unit is stored. Therefore, if an identifier is detected for the predetermined control information unit stored at a position of a predetermined one of the data frames in the data frame groups, it can be confirmed whether or not the predetermined control information unit has been detected at a proper data frame position. When detecting control information units stored in the unit storage regions including the spare data frame and access a control information string, even if an access operation is erroneously performed with a synchronized timing associated with erroneous detection of the specific control information unit being deviant from the data frames in which the control information units are stored, access of a control information string can be made accurately by quickly and reliably detecting a deviation in frame management and performing an access operation of a specific control information unit. Thus, recuperation from the deviation in frame management is accelerated and a considerable contribution to enhancement of TAT in access of LPP information is made.
Further, according to another aspect of the invention, there is provided an information access device that detects control information units at a synchronized timing based on detection of a specific control information unit included in a control information string when access the control information string that is added to an information unit composed of a predetermined number of data frame groups on an information storage medium and that has the control information units divided as basic units and stored in unit storage regions in which one of the data frames is a storage region and in which one or more of the other data frames are spare data frames for a spare region, wherein the information access device comprises a setting portion for setting a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and a discordance detecting portion for detecting discordance unless the control information units are detected in one-to-one relation to each of the unit storage regions including the data frame corresponding to the identifier, and wherein redetection of the specific control information unit is carried out based on an output from the discordance detecting portion.
Further, according to another aspect of the invention, there is provided an information access method in which control information units are detected at a synchronized timing based on detection of a specific control information unit included in a control information string when access the control information string that is added to an information unit composed of a predetermined number of data frame groups on an information storage medium and that has the control information units divided as basic units and stored in unit storage regions in which one of the data frames is a storage region and in which one or more of the other data frames are spare data frames for a spare region, wherein the information access method comprises a setting step for setting a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and a discordance detecting step for detecting discordance unless the control information units are detected in one-to-one relation to each of the unit storage regions including the data frame corresponding to the identifier, and wherein redetection of the specific control information unit is carried out based on an output from the discordance detecting step.
Further, according to another aspect of the invention, there is provided an information storage medium access system comprising a control information access portion that detects control information units at a synchronized timing based on detection of a specific control information unit included in a control information string when access the control information string that is added to an information unit composed of a predetermined number of data frame groups on an information storage medium and that has the control information units divided as basic units and stored in unit storage regions in which one of the data frames is a storage region and in which one or more of the other data frames are spare data frames for a spare region, wherein the control information access portion comprises a setting portion for setting a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and a discordance detecting portion for detecting discordance unless the control information units are detected in one-to-one relation to each of the unit storage regions including the data frame corresponding to the identifier, and wherein redetection of the specific control information unit is carried out based on an output from the discordance detecting portion.
In the information access device, the information access method and the information storage medium access system, the setting portion sets a corresponding identifier for each of the data frames on the basis of the data frame in which the specific control information unit is stored, and the discordance detecting portion detects that the control information units are not detected in one-to-one relation to each of the unit storage regions including the data frame corresponding to the identifier. Redetection of the specific control information unit is carried out based on an output from the discordance detecting portion.
Thereby the control information units are stored in one of the unit storage regions. Therefore, a deviation in frame management can be confirmed if a relation between the detected control information unit and the unit storage regions is confirmed by the identifier corresponding to the control information unit.
Further, since this confirmation can be carried out through detection between adjacent control information units, it is possible to quickly and reliably confirm a deviation in frame management and accurately reproduce a control information string. Thus, recuperation from the deviation in frame management is accelerated and a considerable contribution to enhancement of TAT in access of a control information string is made.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.